Metal anode for electrolytic cells



April 21, 1970 E. DCNGES ET AL METAL ANODE FOR ELECTROLYTIC CELLS Filed Sept. 18, 1967 5 Sheets-Sheet 1 INVENTORS ERNST obwess HELMUT HUND M,%% m/ ATTQRNEVS A ril 21, 1970 E. DONGES ETAL 3,507,771

METAL ANODE FOR ELECTROLYTIC CELLS T 5 Sheets-Sheet 2 Filed Sept. 18, 1967 /4/ 3 I l l I r I 'L'JUUUIJL'UUUL INVENTORS ERNST DifiNGES T.HUND M,M4

ATTORNEYS HELMU E. DCNGES ETA!- METAL ANODE FOR ELECTROLYTIC CELLS April 21, 1970 Filed Sept. 18, 1967 a 5 Sheets-Sheet 3 INVENTORS ERNST 06M GES UND HE MUT H 8&2;

ATTORNEYS I April 21, 1970 E. DONGES ErAL 3,507,771

METAL ANODE FOR ELECTROLYTIC CELLS I SSheets-Sheet Filed Sept. 18, 1967 INVENTORS 5 0 EM. S m H OH N D T R UO 0 SM I n N A E April 21, 1970 E. DGNGES ETAL 3,507,771

METAL ANODE FOR ELECTROLYTIC CELLS Filed Sept. 18, 1967 5 Sheets-Sheet 5 FIG. 10

INVENTORS ERNST D'ONGES ATTORNEYS United States Patent METAL ANODE FOR ELECTROLYTIC CELLS Ernst Diinges and Helmut Hund, Frankfurt am Main,

Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany Filed Sept. 18, 1967, Ser. No. 668,399 Claims priority, appliclatigr; 3(igrmany, Sept. 30, 1966,

Int. Cl. B011; 3/ 04; C23!) 5/74 US. Cl. 204284 6 Claims ABSTRACT OF THE DISCLOSURE Metal anode suitable for electrolyzing aqueous alkali metal chlorides in horizontal electrolytic cells having a mercury cathode, in which anode no adhering gas films are formed at the phase boundary. The anode has such a shape that the brine continuously circulates, thus rapidly transporting gas from the phase boundary.

It appeared, however, that anode surfaces of this type, even when they are provided with numerous holes for the gas escape, have practically no advantage over graphite anodes as to the separating voltage and, especially with current densities which are higher than usual, they operate in an unfavorable manner since adhering gas films are formed causing additional gas bubble resistances and thus concentration polarizations at the phase boundary, whereby the cell voltage and, at a short distance between the electrodes, even the current efliciency are reduced.

Moreover, German Auslegeschrift (DAS) No. 1,235,277 discloses an arrangement of anodes, in which the flat metal anode is provided with a joint piece intended to force the brine through the gap between the anode and the cathode in order to bring about a sufficiently high brine concentration in the electro gap. This, however, only slightly affects the gas film so that even this arrangements reduces the current efliciency at a short distance between the electrodes.

The present invention nowrelates to a metal anode covered with a layer of platinum, preferably titanium, for electrolyzing alkali metal chlorides in electrolytic cells having a mercury cathode, which anode consists of U-shaped profiles arranged in ranks at a short distance from one another, each of which comprises two flanges ending in symmetrically folded portions which form with those of the adjacent profiles an obtuse angle, the vertex of which being provided with a slot and the web of the profile being provided with a range of holes or a slot.

The folded portions of two adjacent profiles may form any obtuse angle in the range of from +120 to l20 The slot along the vertex has a width ranging from 1 to 4 millimeters, preferably it is 2 millimeters. The web of the profile has a width in the range of from 2 to 10, preferably from 3 to 5 millimeters and the height of the flange ranges from 5 to 50, preferably from 15 to 25 millimeters. The distance between two adjacent profiles of a metal anode is in the range of from 5 to 30, preferably from 12 to 20 millimeters. The holes in the web of a profile, through which the gas and the spent brine escape, preferably have a diameter which corresponds to the width of the web. The surfaces of the folded portions facing the cathode are lined with a layer of precious metal, preferably platinum, iridium or platinum-iridium, which reaches up to about 2 millimeters into the U-shaped profile.

Embodiments of the present invention are anodes consisting of a number of U-shaped profiles as well as anodes shaped in folds from a single metal sheet.

Advantageous embodiments of anodes according to the invention are illustrated diagrammatically by way of example in the accompanying drawings.

Referring to the drawings,

FIGS. 1 to 3 are perspective views of sections of the anode.

FIG. 4 is a cross-section of the anode provided with a device for current supply.

FIG. 5 is a perspective view of sections of two profiles, showing the flow of the brine in the anodes shown in FIGS. 1 and 2.

FIG. 6 is a perspective view of sections of two profiles, showing the flow of the brine in the anode shown in FIG. 3.

FIG. 7 is a top view of an anode provided with a device for the current supply.

FIGS. 8 and 9, each shows a perspective view of two profiles with the folded portions of their flanges forming the extreme obtuse angle.

FIG. 10 shows the current density as a function of voltage.

In each of the figures, web 1 is limited by flanges 2 whose folded portions 3 have slots 4 parallel to their folding lines, through which slots the brine circulates. Web 1 is provided with holes 5, through which the brine circulates likewise. The distance between the individual U-shaped profiles is indicated by 6.

In an embodiment of the anode according to FIG. 2, the fresh brine poor in gas bubbles passes between the individual U-shaped profiles into slot 4, it is fllen divided into two partial streams 7 and 8 which flow along the phase boundary and which unite within the U-shaped profiles to form a stream 9 rich in gas bubbles, which escapes from the anode through holes 5.

In FIGURE 10, the current density measured in the individual elements of an anode, is shown as a function of voltage. The individual elements had the following d1mensions: length of the profile: 250 millimeters; width of the web 1: 4 millimeters; height of the flange 2: 15 millimeters; width of the slot 4: 2 millimeters; folded portion 3 formed with the corresponding portion of the adjacent profile an obtuse angle of The currentvoltage curve was fixed at a cell temperature of 70 C., a medium brine concentration of 300 grams of NaCl/liter of brine and an amalgam discharge concentration of 0.12% of sodium. The current efliciency Was 96.5%, the distance of the remotest point of the anode from the cathode being about 2 millimeters. When the curve I measured on the anode of the invention was compared with curve II measured on an anode having no slots (4), for example the cell voltage diiference between curves I and II was 0.3 volt at a current density of 10 ka./square meter. This corresponds to a saving in energy of 7% by the anode of the invention in comparison with the anode of the prior art.

Compared with the anodes hitherto known, the anode of the invention has the following advantages:

The gas bubble resistances mentioned above and the concentration polarizations resulting therefrom only occur in a limited extent. In the arrangement of the invention, the brine necessarily circulates about the individual profiles of which the anode consists, owing to their different partial densities. Thus, fresh brine poor in gas bubbles continuously passes the phase boundary whereas the same amount of spent brine rich in gas bubbles escapes from the phase boundary. During this short period of escape, the finely divided small gas bubbles accumulate outside the phase boundary to form big gas bubbles which are then withdrawn in usual manner. Turbulences in the brine, which adversely affect the electrolytic process, do not occur in. the arrangement of the invention.

What is claimed is:

1. A metal anode covered with a layer of platinum, suitable for electrolyzing alkali metal chlorides in electrolytic cells having a mercury cathode, which anode consists of inverted U-shapcd profiles arranged in ranks at a short distance from one another, each of which comprises two flanges ending in symmetrically folded portions which form with those of the adjacent profiles an obtuse angle, the vertex of which is a slot and the web of each individual profile is provided with a range of holes or slots.

2. The metal anode of claim 1, wherein the folded portions of two adjacent profiles form an obtuse angle in the range of from +120 to 120.

3. The metal anode of claim 1, wherein the slot along the vertex has a width ranging from 1 to 4 millimeters.

4. The metal anode of claim 1, wherein the web of a profile has a width in the range of from 2 to 10 millimeters, and the flange has a height ranging from 5 to 50 millimeters.

5. The metal anode of claim 1, wherein the distance between the adjacent profiles is in the range of from 5 to 30 millimeters.

6. The metal anode of claim 1, wherein the metal is titanium.

References Cited UNITED STATES PATENTS 2,744,864 5/ 1956 Miiller 204220 2,974,098 3/1961 Oliver 204288 3,062,733 11/1962 Lynn et al. 204284 XR 3,174,923 3/1965 Golden et al 204-220 FOREIGN PATENTS 748,864 12/1966 Canada.

JOHN H. MACK, Primary Examiner D. R. JORDAN, Assistant Examiner US. Cl, X.R. 204288, 290 

